Why are you wanting to set up BT Premium email?
https://www.bt.com/help/email/what-is-premium-email-and-how-do-i-get-it-/
Have you tried section 7 of the above link?
Were you a BT Broadband customer and if so did you not have a BTID?
Were you given a BTMail email account from somebody's BT Broadband account?
If you were did you go through the "gift email" process. see link and sub link "how to create and gift etc.
https://www.bt.com/help/email/manage-email-account/account-set-up/how-do-i-create-and-activate-a-ne...
